Skin cancer (basal cell carcinoma, squamous cell carcinoma, and cutaneous melanoma) is the most common form of cancer in the United States. Approximately 90 percent of non-melanoma skin cancers are attributed to UV radiation. Absorption of solar radiation by the skin leads to DNA damage by the formation of cyclobutadiene pyrimidine dimers, pyrimidine (6,4) pyrimidone photoproducts, and single strand breaks.
UV radiation is conveniently divided into three groups (“bands”): UVA (320-400 nm), UVB (280-320 nm), and UVC (200-280 nm).
UVA radiation penetrates more deeply into the skin than does UVB, and leads to suntanning by oxidizing melanin in the skin to produce a dark pigment. UVA constitutes about 90% of UV radiation reaching the Earth's surface.
UVB constitutes about 10% of UV radiation reaching the Earth's surface. UVB radiation is the primary cause of sunburn and skin cancer. UVB is about 1000 times more potent in causing sunburn than is UVA.
UVC is not part of the tanning process. UVC is high energy UV radiation, and would cause significant damage to cells with which it contacted. Fortunately, UVC is absorbed by the Earth's atmosphere.
Sunscreen products are commonly given a sun protection factor “SPF” which correlates to the ability of the product to block UVB radiation. SPF is measured as the ratio of the amount of ultraviolet radiation required to produce minimal pinkness (erythema) in skin covered by a sunscreen, assessed 24 hours after exposure, to the amount of UV radiation required to produce a similar level of pinkness in unprotected skin. The SPF does not indicate the degree of UVA protection for a product.
Skin phototypes are rated on a scale of 1 to 6. The amount of UV radiation that may be absorbed by the skin without causing sunburn may be determined using the following table.
TABLE 1Skin phototypesMinimum erythemal doseSkin phototypeUnexposed skin color(MED) mJ/cm21White15-302White25-403White30-504Light brown40-605Brown60-906Dark brown or black 90-150
Formulations useful for protection against UVA and/or UVB radiation can be divided into sunscreens and sunblocks. Sunscreens are spread onto the skin as an essentially invisible thin film. Sunblocks contain particulates such as titanium dioxide and zinc oxide which physically block ultraviolet radiation. Sunblocks provide broad protection against both UVB and UVA light. They can be cosmetically unacceptable to many people, because they are often messy, visible and do not easily wash off. Chemicals in sunscreens and sunblocks have come under scrutiny, as they have been suspected of generating free radicals.
Historically, various chemical agents have been used in oil, cream, and lotion sunscreen products. PABA (para-aminobenzoic acid) was one of the original ultraviolet B (UVB) protecting ingredients in sunscreens. Recently, PABA has been largely replaced by PABA esters (such as glycerol PABA, padimate A and padimate O) in sunscreens. PABA and PABA esters protect against UVB radiation, but not UVA radiation, the sun's burning rays that are the primary cause of sunburn and skin cancer. Additional commercial UVB blockers include salicylates, homomenthyl salicylate, cinnamates, octylmethoxycinnamate, cinoxate, benzophenones, oxybenzene, sulisobenzene, and anthranilates. UV scattering agents include zinc oxide, titanium dioxide, magnesium silicate, magnesium oxide, kaolin, ferrous oxide, ferric oxide, barium sulfate, and red petrolatum.
Chemicals which block UVA radiation include oxybensone, sulisobenzone and Parsol 1789 (avobenzone).
Various cosmetic formulations containing DNA have been proposed.
“DNA” is a skin restoration product by Wilma Schumann (distributed by About Face International, Inc.). The product contains deoxyribonucleic acid extracted from salmon roe. “DNA” is advertised as a treatment for combating stretch marks and acne. “DNA PLUS” is a gel emulsion of deoxyribonucleic acid, vitamin A, and vitamin E. The vitamins are suggested to protect the skin from the influences of the damaged ozone layer and from ultraviolet rays.
U.S. Pat. No. 5,547,684 describes cosmetic preparations containing DNA-sodium salt useful for the treatment of aging skin and skin problems. The DNA is extracted from various fish reproductive cells using a sodium chloride solution.
U.S. Pat. No. 5,985,333 describes the use of compositions containing DNA-sodium salt for burn and wound treatment. The compositions were proposed to be particularly useful for the treatment of burns resulting from radiation, such as those due to radiation therapy.
U.S. Pat. No. 5,662,889 describes oral compositions containing DNA-sodium salt. The compositions are proposed as mouthwash and toothpaste formulations.
U.S. Pat. No. 5,194,253 describes an aqueous gel containing alkaline salt or ammonium salt of hyaluronic acid, mineral or organic salt of high molecular weight DNA, and a hydrophilic polymer. The gel is proposed as a facial mask. The mask is alleged to have the following beneficial properties: powerful anti-wrinkle effect; improvement in the sebaceous secretion and regulation of the superficial hydro-lipid film; considerable increase in the elasticity and in the firmness of the teguments; the effect of an exceptional increase in the freshness of the complexion; very effective photo-protection power; and favorable structural modifications, detectable by appropriate examination, of the dermo-epidermal constituents.
U.S. Pat. No. 4,707,354 describes sunscreen, protectant, and moisturizing dermatological compositions
There exists a need for improved sunscreen formulations that confer protection from harmful ultraviolet radiation using biocompatible chemicals.